The stakes are high in this primary for 3.7 million Puerto Ricans, who cannot cast a ballot in the general presidential election. For them, the primary represents the only practical way they can affect the outcome of the election.

"Since they can't vote in general, they tend to be excited about the opportunity to make an impact now, so turnout will likely be high and may be an opportunity for winners to demonstrate their appeal to Hispanics," said Justin Velez-Hagan, founder and executive director of the National Puerto Rican Chamber of Commerce.

Puerto Rico can arguably make a difference in the Republican primary. The commonwealth has more delegates than Vermont and as many as Maine. It also represents a chance for Sens. Marco Rubio and Ted Cruz as well as Ohio Gov. John Kasich to gain ground on real estate mogul Donald Trump.

Puerto Rico's three super delegates have already endorsed Rubio, which could indicate that the island is ready to back the young Cuban-American. Underscoring the primary's importance, Rubio will be campaigning in San Juan on Saturday.

A win in Puerto Rico for Rubio could provide a boost in Florida, where the senator is currently trailing by double-digits in the polls to Trump, heading into its winner-take-all primary on March 15.

Puerto Ricans can vote in the general election if they reside on the mainland, and record numbers of Puerto Ricans have been fleeing the island in recent years because of the ongoing economic woes. Many of them have moved to Florida's I-4 corridor in the center of the state, which is now home to a large Puerto Rican population.

The territory's Democratic primary won't be held until June, 67 delegates up for grabs, more than four of the Super Tuesday states.

A strong turnout is expected Sunday. In fact, thousands of inmates in prisons across the island have already cast their early ballots, according to the Associated Press.

At least, 6,500 of the 11,500 prisoners are registered to vote, and government officials say that turnout has been strong. Puerto Rico has allowed inmates to vote since the 1980s, and joins Maine and Vermont as the only places where prisoners can vote.

"This is a democracy, and everyone should be able to exercise their right to vote," Edgardo Rodriguez, 46, a first-time voter, told the AP. "Puerto Rico needs help ... The crisis is choking us."